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Tritium Science & Engineering/Materials Science & Technology
Hydrogen Separating Membranes for Coal Gas Reforming
Stephen N. Paglieri & Stephen A. BirdsellLos Alamos National Laboratory
Los Alamos, New Mexico, U.S.A.
Tritium Science & Engineering/Materials Science & Technology
Overview
■ Background– Hydrogen separating membranes
■ Coal-gas reforming in a PMR– Where membranes fit into Vision 21
■ Fabrication and testing of palladium composite membranes
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What’s so special about palladium?
■ Palladium (Pd) can absorb many times its volume in hydrogen
■ Pd is catalytically active for hydrogen dissociation
■ Alloys of Pd are durable
*http://www.psc.edu/MetaCenter/MetaScience/Articles/Wolf/Wolf.html
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Vision 21
■ Part of Vision 21 entails coal gasification to recover both H2 for fuel cell use and CO2 for sequestration
– http://www.netl.doe.gov
■ A PMR accomplishes this in a single unit operation
GasificationPyrolysis
Combustion
PalladiumMembrane
Reactor
Pure H2 Fuel CellReactor
ConversionCO2-richstreamSyngas
Products
TurbineSyngas
Conversion
ScrubbingSequestration
EnvironmentalControls
PowerHeat
Chemicals
ProductsEnergyConversion
FuelConditioning
CoalNatural gas
BiomassOxygenSteam
SulfurRemoval
ElectricityHeat
Chemicals
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Scale-up issues for Pd membranes■ Cost
– price of Pd is ~$150/ounce (April, 2003)– thickness of Pd film will be < 2 µm for $50-100/ft2
■ Poisoning by process stream impurities– unsaturated hydrocarbons, H2S, carbon monoxide (CO)– should be regeneratable in steam or air
■ Embrittlement– resistance to thermal cycling– α → β (α’) phase transition
■ Leak-free sealing
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How do we address these problems?
■ Cost– thin films of Pd on hydrogen-porous supports– minimize Pd film thickness
■ Poisoning– remove most H2S up front– PdCu40 is sulfur resistant
■ Embrittlement– Pd alloys reduce distortion upon hydriding/dehydriding
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Types of composite configurations
■ Refractory metals have high hydrogen permeabilities– surfaces readily poisoned– must coat with Pd on both sides of metal foil or tube– ion-cleaning in-situ followed by sputter deposition of Pd
■ Pd on a porous support– porous metal supports
■ easier to weld into a module■ available pore sizes take thick Pd coatings (>20 µm) to plug
– porous ceramics■ possess high temperature stability■ commercially available tubes with well-defined pore sizes■ α and γ-alumina, titania, zirconia
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Palladium alloys■ Increased hydrogen permeability and durability■ PdAg23 (weight %)
– tubes (100 µm thick) commonly used to purify hydrogen for semiconductor industry and hydrogen isotope recovery
– grain coarsening during operation at higher temperatures
■ PdRu6– higher melting point metal imparts high-temperature stability and
strength
■ PdCu40– sulfur resistance– D.L. McKinley, U.S. 3,439,474 (1969)– D.J. Edlund
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Fabrication of a Pd-Cu Composite Membrane
■ Sequentially deposit Pd and then Cu■ Anneal to promote metallic interdiffusion
– > 350°C■ Characterization
– hydrogen flux and permselectivity– thickness: SEM, EPMA– composition: EDX, XRD– depth profiling: XPS, AES, Rutherford backscattering
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Preparation of Pd/Ceramic Membraneclean ceramic
membrane
seal ends of ceramic membrane with high temp. glaze
Sensitize surface w/SnCl2 solution
activate or seed surface with Pd crystallites
plate in aqueous solution ofPd-amine complex andreducing agent (N2H4)
• Surface of GTC 998 0.2 µm symmetric Al2O3 Tube
»Scalebar is 2 µm
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Sensitizing/Activating
■ Must catalyze surface of non-conductor to initiate deposition
■ Sensitization w/SnCl2
■ Activation w/PdCl2
■ Water rinse
Cl- Sn2+ Cl- Cl- Pd2+ Cl-
Al Al Al
O Oδ- δ-
Al Al Al
O Oδ-
Sn2+
Al Al Al
O O δ-
Sn4+
Clδ- PdClδ-
M. Charbonnier et al. J. Electrochem. Soc. 143(2) 472 (1996).
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Membrane Preparation
■ Ends of porous tube are glazed to prevent gas bypass of selective layer
■ Electroless plating set-up enables solution circulation while membrane is immersed in sucrose solution
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Pd-Cu/Alumina Composite Membrane
■ Image of a broken membrane showing copper layer
■ Membrane is sealed into the module using compression fittings with graphite ferrules
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Test Module
■ 3 thermocouples on both the inside and outside of membrane
■ Catalyst packed inside the Pd-composite membrane
■ Max T = 550°C■ Max P = 250 psig
D = 0.39”
Pd/aluminamembrane
ID = 0.24”L = 2-10”
3/8”-1/4” Swagelokreducing unionw/graphite ferulles
catalyst
1/4” SS tubing
1/4” SS tubing
Feed (H2O, CO, H2S)Max P = 250 psig
Copper gasket
1/2” flange
2.75”
1/4” SS Swagelokbored through to enablepenetration of 1/4” tube
1/16” SS Swagelok forthermocouple penetration
1/4” SS Swagelokbored through to enablepenetration of 1/4” tube
1/4” SStube forpermeate
H2 Permeate
Tube 1.5”
Length of SSTube to weldedon flange L = 15”
1/4” SStube forpermeate
1/16” SS Swagelokfor thermocouplepenetration
Maximum system temperature = 550 CMaximum shell pressure = 30 psig
1/4” SS tube forconection to membrane (retentate)
Retentate
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Hydrogen & Argon Flux vs. Time through Pd-Cu/Alumina Membrane
■ Hydrogen flux increases as Pd and Cu interdiffuse
■ ∆P = 100 psi■ αH2/Ar ≅ 68
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0 5 10 15
Time (days)
Flux
[mol
(ST
P)/m
2s]
Hydrogen FluxArgon Flux
~335C ~355C
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Pd/refractory foil/Pd Composite
HYDROGENMOLECULES
HYDROGENATOMS
HYDROGENMOLECULES
Pd
PALLADIUM
PALLADIUM
FEED GAS
ULTRA-PURE HYDROGEN
Group V Metal
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Pd/V-alloy/Pd membrane■ Palladium coating is
very thin– 1000 Å
■ Alloy of vanadium reduces hydrogen embrittlement
■ Welded into the shape of a tube
– SS VCR fittings– Flux = 0.4 sccm/cm2•min @
∆P = 5 psi
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AES Depth Profiles of Pd on V-CuAuger Depth Profile
0
500
1000
1500
2000
2500
3000
0 1000 2000 3000 4000 5000 6000 7000 8000
Time, sec.
Inte
nsity
, A
PPH
Pd
V
Cu
MPDVCU.A0
Auger Depth Profile
0
500
1000
1500
2000
2500
0 2000 4000 6000 8000 10000 12000
Time, sec.
Inte
nsity
, A
PPH
Pd
V
Cu
C
O
MCUVPD.ASpringer/LAN
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Future Work
■ Membrane reactor■ Pack catalyst around membrane■ Low, medium, and high temperature water-
gas shift■ Fe-Cr-Cu oxide, Cu-ZnO catalysts■ Test sulfur resistance of membrane
materials
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Acknowledgements
■ Membrane development work was funded by the US DOE, Office of Fossil Energy
■ Rob Dye, David Pesiri, Bob Springer, DonGettemy, John Moya, Stan Bennett, Stephen Cole, Jerry Schobert, Mike Brooks, Frank Smith, Ron Snow, Robert Barbero, Felix Garcia, Fino Armijo, John Valdez, Vincent Hesch, and Kevin Hubbard